Coupling system for carrier currents



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ATTORNEY Patented Nov. 3, 1942 COUPLING SYSTEM FOR CARRIE CURRENTS Bernard E. Lenehan, Bloomfield, N. J assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 5, 1939, Serial No. 271,954

' 3 Claims.

My invention relates to coupling systems for carrier current, and it has particular relation to the use of a superimposed carrier current, of an oscillatory type, for protecting polyphase transmission lines against faults, by properly controlling the opening of the line-sectionalizing circuit-breakers.

The conventional coupling system for carrier current is to use a shunt feed, to the line, through coupling capacitors, and touse series blocking impedance in the line, to confine the carrier current more or less to the protected line-section. Although this conventional coupling system has advantages when applied to high-voltage and medium-voltage lines, it has nevertheless certain disadvantages particularly in connection with lines of lower voltages, such, for example, as 26 kilovolts.

It is an object of my invention to feed the carrier current to and from the line through a serially connected inductive coupling, and to use tuned shunt-connected blocking impedances for more or less confining the carrier current to the protected line-section and for providing a good return-path for the carrier current. As a result of this innovation, I reduce the required size of the shunt-connected capacitor to a value making it possible to use a condenser-bushing on an oil circuit-breaker for the capacitor part of the tuned shunt-connected blocking impedances; I reduce the required amount of excess-voltage protection; I reduce the required amount of serially connected inductance which must be inserted in the protected line-section; and I am enabled to obtain band-pass tuning-effects by proper coupling.

It is a still further object of my invention to utilize concentric air-core coils for the series coupling, with sufficient spacing between the two coils for withstanding the line-voltage.

It is a still further object of my invention to provide a series coupling system for carriercurrent translating-apparatus of adjustable frequency, with a carrier-current cable for connecting the translating-apparatus to the coupling device, and with means for adjusting the tuning of the coupling to the frequency of the carriercurrent translating-apparatus without disturbing the matched balance between the effective surge-impedance-burden of the transmissionline conductor, which should be matched against the effective impedance of the carrier-current cable.

With the foregoing and other objects in view,

erly withstand the line-voltage.

my invention consists in the apparatus, combina- 55 tions, circuits, systems and methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Figure 1 is a simplified diagrammatic view of circuits and apparatus illustrating an application of my invention,

Fig. 2 is a similar view illustrating a modification, and

Fig. 3 is a somewhat diagrammatic structural view illustrating the physical nature and construction of the coupling coils.

In Figure 1, I indicatev the carrier-current equipment at one end of a protected line-section I of a threephase transmission-line or electric power-line, having phase-conductors a, b and c. It is contemplated that similar equipment will be utilized at both ends of the protected linesection, so that an illustration and description of one will sufiice for both. The protected linesection I is connected to the station-bus 2 through an oil circuit-breaker 3 which is provided with a trip-coil 4, which must be tripped whenever there is a fault on the protected linesection. I have also schematically indicated an adjustable-frequency carrier-current aggregate or translating-apparatus 5, comprising a transmitter and a receiver, which is utilized, in any desirable or well-known manner, either in the automatic protective control of the circuitbreaker trip-coil 4, or in the supervisory control operation of the transmission system, or for communication purposes in the management of the transmission-system, or for a plurality of these uses.

In accordance with my invention, the carriercurrent equipment 5 is coupled to the protected line-section I through a series inductive coupling-means 6 comprising a relatively smalldiameter air-core coupling-coil I (Fig. 3) which is supported on insulators 8 and connected in series with one phase-conductor, such as phase 0, of the protected line-section I, and a relatively large-diameter air-core coupling-coil 9 which is insulatedly mounted on a supporting cradle l0 so as to be substantially concentric with respect to the line-connected coil 1. The difference between the radii of the two coils l and 9, as indicated at A in Fig. 3, should be such as to prop- The line-connected coil 1 is shunted by a tuning-capacitor l I, which should be variable in order to admit of accommodation for a certain range of carriercurrent frequencies.

The large-diameter or low-voltage coil 9 of the coupler is connected in series with a separate variable inductance device l2 and a fixed capacitor I3, and the aggregate comprising the largediameter coupling coil 9, the variable inductor l2 and the fixed capacitor I3 is serially joined to the carrier-current aggregate 5 by means of any suitable type of carrier-current cable I4 which may be of the coaxial-conductor type, or the twisted-line type, or the sheathed type, or any other type suitable for carrying currents of high frequency.

As previously intimated, it is quite desirable, in order to avoid shock-excitation, as is well known, to utilize a coupling device which matches the effective impedance of the cable I4 against the effective shock-impedance of the transmis sion-line l, and my utilization of a fixed-ratio coupling-device 6, with a shunt-connected variable capacitor II on the high-tension side, and a separate serially connected variable inductance device l2 on the low-tension side, makes it pos- H sible to adjust the coupling device to the frequency of the carrier-current equipment without disturbing the matched-impedance effect, it being understood that it is necessary to have carrier currents of difierent frequencies, in different portions of the transmission-system, in order to segregate the carrier-current control to better advantage. This particular tuning method, for the coupler 6, also results in obtaining bandtunlng effects which obviate the necessity for very precise or exact tuning to the carrier-current frequency.

One of the line-conductors, such as the conductor c, is thus utilized to carry the superimposed carrier current from one end of the protected line-section to the other end, and it is necessary to provide some means for providing a return-conductor for the carrier current. In Fig. 1, this return-conductor is the ground or earth 20, and in Fig. 2 the return conductor is 4-.

another phase-conductor, such as the conductor b, of the protected line-section In either case, the return-conductor is at a difierent line-irequency potential than the serially coupled conductor c.

In accordance with my invention, a tuned shunt-circuit is provided for effecting an easy path for the flow of carrier-frequency currents from the serially coupled conductor 0 to the return-conductor 20 or b, as the case may be. 5;

In Fig. 1, I utilize a capacitor-bushing, on the oil circuit-breaker, where the line-conductor c enters the circuit-breaker casing, as diagrammatically indicated at 2|, as the capacitor part of a tuned shunting-circuit which is completed ductor c and the line-conductor b which is utilized as the return-conductor for the carrierfrequency current. In either event, the variable tuning-inductance 22 should be shunted by a suitable excess-voltage protective device, such as a spark-gap 24, but by reason of the small size of the serially connected capacitor 2|, or the serially connected capacitors 2| and 23, the duty imposed upon the spark gap 24 is relatively slight.

It will be noted that the series coupling-device 6 should be connected on the line-side of the tuned shunt-circuit 2|22 or 2|-2223, as the case may be, so that the two series inductive coupling-means 6, at the two ends of the protected line-section I, shall be included between the two tuned shunt-connected circuits 2|-22 or 2 |2223 which are geographically separated at opposite ends of the protected line-section.

While the utilization of my herein-described invention, in lieu of the conventional shunt coupling of the carrier-current equipment, has certain advantages, as previously pointed out, I desire to emphasize, at the present time, the saving in the protective equipment 24 which is made possible by my use of tuned shunting-circuits and series inductive coupling-devices. My invention, however, at the present time appears to be limited to application to transmission-lines of the lower range of voltages, because, for transmission-lines of extremely high voltage, the requisite insulating-spacing A in Fig. 3 becomes excessive.

While I have illustrated my circuits in two forms of embodiment which at present seem preferable, and while I have illustrated the physical forms of my inductive coupling device in a particular design which at present seems preferable, I wish it to be understood that my invention is not limited in either of these respects, but is subject to a considerable latitude of modification, as will be obvious to those skilled in the art, I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language and the prior art.

I claim as my invention:

1. A high-frequency coupling-device comprising a relatively small-diameter air-core couplingcoil, a relatively large-diameter air-core couplingcoil insulatedly mounted substantially concentrically with respect to said small-diameter coupling coil, said coils being both fixed and of a fixed number of turns, a coupled circuit serially connected to one of said coupling coils, an adjustable capacitance-device connected in shunt relation to said one of said coupling-coils, and a separate adjustable coil, a fixed capacitance device, and an adjustable-frequency high-frequency device serially connected to the other coupling coil, the adjustable capacitance-device and the adjustable coil being tunable in accordance with the adjustable frequency of the high-frequency device, the eiiective shock-excitation impedances of the coupled circuit and the circuit containing said high-frequency device being substantially matched at all times regardless of the tuningadjustments of said adjustable capacitancedevice and said adjustable coil.

2. The combination, with a commercial-frequency alternating-current power-line having a line-conductor at a predetermined line-frequency potential with respect to ground, of an adjustable-frequency device of relatively high frequency so associated with said power-line so as to be substantially insulated from said predetermined line-frequency potential with respect to ground, and a high-frequency coupling device comprising a relatively small-diameter air-core couplingcoil serially connected in said conductor of said power line, a relatively large-diameter air-core coupling-coil insulatedly mounted substantially concentrically with respect to said line-connected coupling coil, said coupling coils being both fixed and of a fixed number of turns, the radial separation between said coupling coils being suflicient to withstand said predetermined line-frequency potential with respect to ground, and a separate adjustable coil, a fixed capacitance device and said adjustable-frequency high-frequency device serially connected to the large-diameter coupling coil, the adjustable coil being tunable in accordance with the adjustable frequency of the highfrequency device, the effective shock-excitation impedances of the circuit containing said conductor of the power-line and the circuit containing said high-frequency device being substantially matched at all times regardless of the tuning-adjustment of said adjustable coil.

3. The combination, with a commercial-frequency alternating-current power-line having a line-conductor at a predetermined line-frequency potential with respect to ground, of an adjustable-frequency device of relatively high frequency so associated with said power-line so as to be substantially insulated from said predetermined line-frequency potential with respect to ground, and a high-frequency coupling device comprising a relatively small-diameter air-core couplingcoil serially connected in said conductor of said power line, a relatively large-diameter air-core coupling-coil insulatedly mounted substantially concentrically with respect to said line-connected coupling coil, said coupling coils being both fixed and of a fixed number of turns, an adjustable capacitance-device connected in shunt relation to said line-connected coupling coil, the radial separation between said coupling coils being sufficient to Withstand said predetermined linefrequency potential with respect to ground, and a separate adjustable coil, a fixed capacitance device, and said adjustable-frequency high-frequency device serially connected to the largediameter coupling coil, the adjustable capacitance-device and the adjustable coil being tunable in accordance with the adjustable frequency of the high-frequency device, the effective shockexcitation impedances of the circuit containing said conductor of the power-line and the circuit containing said high-frequency device being substantially matched at all times regardless of the tuning-adjustments of said adjustable capacitance-device and said adjustable coil.

BERNARD E. LENEHAN. 

